This invention relates to a method for the froth flotation of coal and, particularly, to the use of an oxygen containing compound as a conditioner for coal.
Combustible carbonaceous solid material ("coal") is inherently found in deposits containing non-combustible mineral matter. Although large fragments of the non-combustible materials can be removed by screening or conventional gravity concentration techniques such as centrifugation, froth flotation is more commonly employed to remove the coal from the finer non-combustible materials. In a conventional froth flotation process, a slurry of the coal in an aqueous liquid is separated from non-combustible materials present in the coal ore by introducing a gas (or providing a gas in situ) in the liquid to produce a frothy mass, with the froth containing the coal being recovered and non-combustibles advantageously being maintained suspended (unfrothed) in the slurry.
In the froth flotation process, it is desirable to recover as much coal as possible while effecting the recovery in a selective manner, i.e., minimizing the amounts of undesirable material or ash in the froth. Various flotation agents are used in the frothing process to maximize selective recovery of coal. For example, the froth flotation process is often conducted in the presence of a frother and collector, commonly a hydrocarbon based oil such as kerosene, to enhance the flotation process. The frother assists in maintaining a stable foam and the collector preferentially wets some of the solid particles (e.g., the particles of coal values) which enhances the recovery of the wetted particles and improves the overall flotation process.
A conventional frother used widely in commercial operations is methyl isobutyl carbinol. Many other alcohols are also disclosed as being useful as frothers in a coal flotation process (See, specifically, U.S. Pat. Nos. 4,272,364; 4,377,473; 4,504,385; and 4,582,596).
Many coals, e.g., coals in which the surface has been at least partially oxidized such as sub-bituminous coals, are difficult to float. This results in an undesirable loss of significant amounts of combustible material in the tail from the flotation.
Increases in the amounts of this so-called "hard-to-float" coal recovered in the froth can be improved by increasing the concentration of the oil-type collector employed in the flotation process. Unfortunately, acceptable recovery can often be effected only using such high amounts of the oil-type collector that significant amounts of the non-combustible matter are floated with the coal. Sun suggests in Trans. AIME, 199:396-401 (1954), that fatty amines can be utilized as co-collectors in the flotation of oxidized coals to effect enhanced recovery. However, even these amine collectors float substantial amounts of ash along with the coal and effect only partial recovery of combustible material.
It has also been suggested to employ ethylene oxide, propylene oxide or butylene oxide as a conditioner for the recovery of coal using froth flotation processes. (See, specifically, Russian Pat. No. 810285). Unfortunately, ethylene oxide, propylene oxide and butylene oxide are not particularly effective in enhancing the froth flotation process. This is particularly true when the coal is highly oxidized.
A variety of other materials have been suggested for use to beneficiate coal in a froth flotation process. Such materials include the condensation product of a fatty acid or fatty acid ester with the reaction product of a polyalkylenepolyamine and an alkylene oxide (U.S. Pat. No. 4,305,815); the condensation product of an alkanolamine and a fatty acid or fatty acid ester (U.S. Pat. No. 4,474,619) and the reaction product of the condensation product of diethanolamine and a C.sub.10-24 fatty acid with a C.sub.1-4 monocarboxylic acid (U.S. Pat. No. 4,330,339). These materials can be effectively employed in the flotation of coal and are capable of the selective recovery of coal over ash at excellent rates of recovery. However, the fatty acid component of the conditioner is subject to variation in cost. In addition, further improvements in the selectivity of the froth flotation process or in the rate of coal recovery, particularly with highly oxidized coals, are always desirable.
Therefore, it is desirable to provide an alternative method for conditioning or beneficiating coal being recovered in a froth flotation process.